Trapezoid train:

You can do the same thing with the trapezoid example:

n=# of trapezoids p = perimeter
1 5
2 8
3 11
4 14

equation: p = 3n + 2

This makes sense with the trapezoids because:

The top and the bottom add 3 to the perimeter for each trapezoid, which is 3n units altogether, plus 2 for the ends gives:

p = 3n + 2